Method for producing metal from metal oxide by carbothermic reduction and holed cake used therefor

ABSTRACT

A high-efficiency method for producing metal from metal oxide by carbothermic reduction includes step in which a holed cake is provided, which has a composition comprising a metal oxide, a carbonaceous reducing agent, and a binder, and the holed cake has a plurality of holes. The method continues with step in which the holed cake is placed in a high-temperature furnace for carbothermic reduction, to reduce the metal oxide in the holed cake into a metal.

FIELD

The disclosure relates to a method for producing metal, more particularto a high-efficiency method for producing metal from metal oxide bycarbothermic reduction and a holed cake used therefor.

BACKGROUND

Nowadays, blast furnace (BF) is the most popular commercial ironmakingprocess, in which the raw materials are mainly including sinter, pellet,lump ore and coke, and the product is hot metal which is the source tothe following steelmaking process. However, the BF process requires highquality of the raw materials and the raw materials requires to bepretreated to qualified properties. Coke is made from coking coal bycoking process; fine ore needs to be sintered into agglomeration.Therefore, the ironmaking process via BF is relatively long. Inaddition, coking and sintering process consumes a lot of energy andcause severe pollution. The capital using in the prevention of pollutionis particularly high. Furthermore, the most important thing is that itis very difficult to further reduce the emission of carbon dioxide(CO₂).

Rotary hearth furnace (RHF) process is one of commercial ironmakingprocess by the means of carbothermic reduction. In generally, the metaloxide mixing with carbonaceous material is pelletized into pellets. 1 or2 layers of pellets are charged on the hearth of RHF for reduction.After the pellets are heated, the pellets are induced to the reductionreaction. Finally, the direct reduced iron (DRI) will be obtained.However, the metal iron conversion rate and yield of metal iron of DRIis not high enough. It is because the combustion gas content high CO₂and H₂O which is easy to re-oxidize the reduced iron.

FIG. 1 illustrates the radiation heat receiving behavior of theconventional multi-layer pellet bed in (a) the initial stage of thereduction reaction and (b) under the stage of the reduction reaction. Inorder to improve the shortcomings of the RHF process, increasing thelayers of pellet bed and increasing furnace temperature at the same timeis helpful to prevent the re-oxidization of iron and to increase theyield of metal iron. This is well known and is disclosed. However, thepacking in multi-layer pellet bed is not the perfect method. It isbecause that some of pellets in the middle and bottom layers of bedcannot directly receive the heat radiation. Even through the top layerpellet would be shrinking after reduction, the pellets on the top layersstill shelter the path of radiation transferring into the middle andbottom layer pellets. As shown in FIG. 1, the pellets of the first andsecond layers can receive the radiation heat directly, but the pelletsof the n^(th) layer are shielded by the upper pellets and cannot receivethe radiation heat directly, resulting in a slow reaction rate.Therefore, the pellets of the n^(th) layer cannot receive the radiation,until the upper pellets are heated, reduced, and sintered to shrink. Thepath of radiation is locally opened, and the radiation is graduallytransferred from the upper layer to the next layer of pellets. As thepellets receive the heat, the pellets start reducing, sintering andshrinking.

However, the reduction behaviors of the pellets of different rawmaterials or at different operation temperatures in the furnace arevarious. As shown in FIG. 1(b), the pellets of the n^(th) layer mayswell up or may collapse into powdering. On the other hand, as thereducing conditions are not well controlled, the pellets may even getinto softening and melting during the reduction reaction. Once the abovephenomena occur at the upper pellets, the radiation path leading to thebottom layer will be blocked, causing the radiation fail to be passed tothe next layer of pellets, so the reduction reaction cannot be induced,and a high metal reduction rate cannot be achieved.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present disclosure, ahigh-efficiency method for producing metal from metal oxide bycarbothermic reduction includes step in which a holed cake is provided,which has a composition comprising a metal oxide, a carbonaceousreducing agent, and a binder, and the holed cake has a plurality ofholes. The method continues with step in which the holed cake is placedin a high-temperature furnace for carbothermic reduction, to reduce themetal oxide in the holed cake into a metal.

In accordance with another aspect of the present disclosure, a holedcake has a composition comprising a metal oxide, a carbonaceous reducingagent, and a binder, and the holed cake has a plurality of holes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are understood from the followingdetailed description when reading with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 illustrates the radiation heat receiving behavior of theconventional multi-layer pellet bed in (a) the initial stage of thereduction reaction and (b) under the stage of the reduction reaction.

FIG. 2 shows a flow diagram of a high-efficiency method for producing ametal from a metal oxide by carbothermic reduction according to thepresent disclosure.

FIG. 3 shows a schematic structural view of a holed cake according tothe present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that the following disclosure provides manydifferent embodiments or examples, for implementing different featuresof various embodiments. Specific examples of components and arrangementsare described below to simplify the present disclosure. The presentdisclosure may, however, be embodied in many different forms and shouldnot be construed as being limited to the embodiments set forth herein;rather, these embodiments are provided so that this description will bethorough and complete, and will fully convey the present disclosure tothose of ordinary skill in the art. It will be apparent, however, thatone or more embodiments may be practiced without these specific details.

In addition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly on” another element, there are no intervening elementspresent.

It will be understood that singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms; such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

FIG. 2 shows a flow diagram of a high-efficiency method for producing ametal from a metal oxide by carbothermic reduction according to thepresent disclosure. FIG. 3 shows a schematic structural view of a holedcake according to the present disclosure. Referring to Step S21 shown inFIG. 2, and FIG. 3, a holed cake 30 is provided, which has a compositioncomprising a metal oxide, a carbonaceous reducing agent, and a binder.

The content of the metal oxide is 70 to 90 wt % inclusive, andpreferably the metal oxide is iron oxide, nickel oxide, copper oxide,lead oxide, manganese oxide, tin oxide, potassium oxide, sodium oxide,zinc oxide, or a combination of at least two of the foregoing. In thepresent embodiment, the metal oxide is powdered to improve the metalconversion rate.

In one or more embodiments, the metal oxide is a mineral containing themetal oxide.

The content of the carbonaceous reducing agent is 10 to 30 wt %inclusive, and preferably the carbonaceous reducing agent is carbonblack, activated carbon, coal, coke, graphite, charcoal, or acombination of at least two of the foregoing. In the present embodiment,the carbonaceous reducing agent is powdered to improve the utilizationrate of reducing agent.

The binder is added in an amount of 0.1 to 6% based on the total weightof the metal oxide and the carbonaceous reducing agent.

In the present embodiment, the holed cake 30 is prepared by thefollowing steps: the metal oxide, the carbonaceous reducing agent andthe binder are uniformly mixed to form a mixture; and then the mixtureis disposed in a mold to form the holed cake 30. Preferably, the holedcake 30 has a thickness T ranging from 30 to 150 mm.

The holed cake 30 has a first surface 30A, a second surface 30B, and aplurality of holes 30H. The second surface 30B is opposite to the firstsurface 30A. The holes 30H can or cannot in communication with the firstsurface 30A and the second surface 30B. In the present embodiment, thecross section of the holes 30H is circular. Or, in another embodiment,the cross section of the holes 30H is polygonal.

In the present embodiment, each of the holes 30H has a diameter d, and ato-be-reduced material portion 30M is present between two adjacent holes30H, wherein the to-be-reduced material portion 30M has a thickness t.

Moreover, each of the holes 30H has a center C, and a distance G existsbetween the centers C of two adjacent holes 30H. Preferably, thethickness t of the to-be-reduced material portion 30M is less than thedistance G, such that the to-be-reduced material portion 30M can beheated evenly.

Referring to Step S22 shown in FIG. 2, and FIG. 3, the holed cake 30 isplaced in a high-temperature furnace for carbothermic reduction, wherebythe metal oxide in the holed cake 30 is reduced into a metal. In thisstep, the holes 30H of the holed cake 30 face a heat source of the hightemperature furnace (not shown), to allow the radiation heat to beuniformly transmitted to the holes 30H.

In the present embodiment, a reaction temperature of the carbothermicreduction is 900 to 1600° C. inclusive; and for the purpose of improvingthe metal conversion rate and the metal yield, the reaction temperatureof the carbothermic reduction is preferably 1000 to 1550° C. inclusive.A reaction time of the carbothermic reduction is 30 to 80 min inclusive,and preferably 35 to 45 min inclusive.

In the present disclosure, the holed cake 30 having a plurality of holes30H is used as a raw material for carbothermic reduction, through whichthe problem that the bottom layer of the conventional multi-layerpellets cannot receive the radiation heat can be effectively solved, andthe heat transfer rate inside the material can be increased, therebyenhancing the carbothermic reduction rate at the bottom of the hearth.

The present disclosure is illustrated in detail with the followingembodiments, but it does not mean that the present disclosure is onlylimited to the content disclosed by these embodiments.

Referring to Table 1, which shows the source and chemical composition ofthe metal oxide minerals in the comparative example, and Embodiments 1and 2 of the present disclosure. Referring to Table 2, which shows thesource and chemical composition of the carbonaceous reducing agent inthe comparative example, and Embodiments 1 and 2 of the presentdisclosure.

TABLE 1 Source and chemical composition of the metal oxide minerals inthe comparative example, and Embodiments 1 and 2 of the presentdisclosure. Chemical composition of the minerals (wt %) Total FerrousFerric Magnetic Unburned Mineral No. Source Iron oxide oxide iron Carboncarbon Silica Alumina Waste oxide Solid mixed 71.62 56.80 39.18 0.192.26 Not 0.24 Not #01 material from detected detected steel mill Mineral#01 Brazil 63.14 0.12 90.16 Not 0.06 1.50 5.48 0.72 detected Mineral #02Australia 56.69 0.11 80.86 Not Not 10.37 4.95 2.80 detected detectedChemical composition of the minerals (wt %) Magnesium Calcium PotassiumSodium Mineral No. oxide oxide Manganese Phosphorus Sulfur Titania oxideoxide Waste oxide 0.04 0.28 Not 0.07 0.11 0.010 0.005 0.009 #01 detectedMineral #01 0.04 0.02 0.18 0.048 0.006 0.056 0.008 0.013 Mineral #020.03 0.11 0.05 0.031 0.022 0.133 0.011 0.014

TABLE 2 Source and chemical composition of the carbonaceous reducingagent in the comparative example, and Embodiments 1 and 2 of the presentdisclosure. Industrial analysis (ad) Total Elemental analysis (ad)Reducing moisture Volatile Ash Fixed Total agent Source content mattercontent carbon carbon Hydrogen Sulfur Nitrogen Oxygen Coal #1 Australia2.02 34.66 8.44 54.88 75.84 4.92 0.48 1.8 10.16 Coal #2 China 2.42 5.2113.92 78.45 80.66 0.87 0.22 0.08 Not detected

Comparative Example

In the comparative example, the reduction reaction was carried out witha multi-layer stacked spherical material. Table 3 shows the reductionreaction conditions and the characteristics of the reduced iron producedin the comparative example.

TABLE 3 Reduction reaction conditions and characteristics of the reducediron produced in the comparative example. Metal iron Sample Metal oxideconversion rate Yield of metal iron No. mineral No. Reduction reactionconditions (%) Kg-M · Fe/(h * m²) P-1 Waste oxide Carbon/oxygen ratio(C/O) = 1.1 91.4 65.2 #01 Reaction temperature: 1500° C. Reaction time:65 min P-2 Mineral #01 Carbon/oxygen ratio (C/O) = 1.0 84.2 43.6Reaction temperature: 1500° C. Reaction time: 60 min P-3 Mineral #02Carbon/oxygen ratio (C/O) = 1.1 89.8 48.6 Reaction temperature: 1500° C.Reaction time: 65 min

The content ratio of the metal oxide to the carbonaceous reducing agentin the raw material depends on the carbon/oxygen ratio (C/O). C in thecarbon/oxygen ratio (C/O) is calculated based on the total carbon in thereducing agent, and O in the carbon/oxygen ratio (C/O) is the totalnumber of O atoms in the metal oxide that can be reduced by carbon. Thecarbon/oxygen ratio (C/O) is the atomic ratio of C to O contained in thematerial.

After the metal oxide was mixed with the carbonaceous reducing agentaccording to the carbon/oxygen ratio (C/O), a suitable amount of abinder was added. In the comparative example, the binder was added in anamount of 2% of the total amount of the metal oxide and the carbonaceousreducing agent.

After being mixed uniformly, the raw materials were prepared intopellets of 14 to 17 mm in diameter. The pellets were laid on a hearth ina high-temperature furnace, and about 7 to 8 layers of the pellets werelaid, as shown in FIG. 1. According to the reduction reaction conditionsin Table 3, the maximum reduction reaction temperature in thehigh-temperature furnace was 1500° C. and the reduction reaction timewas 60 min or 65 min.

As shown in Table 3, the metal iron conversion rates for the DRIobtained from the sample Nos. P-1, P-2 and P-3 (where the metal ironconversion rate is defined as the metal iron content of the DRI dividedby the total iron content) are 91.4%, 84.2% and 89.8%, respectively. Theyields of the metal iron (where the yield of metal iron is defined asthe metal iron weight of the DRI divided by the hearth area and then bythe total reduction time) are 65.2, 43.6 and 48.6 Kg-M.Fe/(h*m²)respectively.

Embodiment 1

In Embodiment 1 of the present disclosure, the reduction reaction wascarried out with a holed cake. Table 4 shows the reduction reactionconditions and the characteristics of the reduced iron produced inEmbodiment 1 of the present disclosure.

TABLE 4 Reduction reaction conditions and characteristics of the reducediron produced in Embodiment 1 of the present disclosure. Metal ironSample Metal oxide conversion rate Yield of metal iron No. mineral No.Reduction reaction condition (%) Kg-M · Fe/(h * m²) C-1 Waste oxideCarbon/oxygen ratio (C/O) = 1.0 90.5 90.2 #01 Reaction temperature:1450° C. Reaction time: 35 min C-2 Mineral #01 Carbon/oxygen ratio (C/O)= 1.0 83.2 62.4 Reaction temperature: 1450° C. Reaction time: 35 min C-3Mineral #02 Carbon/oxygen ratio (C/O) = 1.0 95.5 69.6 Reactiontemperature: 1450° C. Reaction time: 35 min

The three metal oxide minerals used in Embodiment 1 are the same asthose in the comparative example, and the mixing ratios of thecarbonaceous reducing agents coal #1 and coal #2 are the same as that inthe comparative example. The binder is also added in an amount of 2%.

After being mixed uniformly, the raw materials were prepared into aholed cake, as shown in FIG. 3. The holed cake has a parameter T ofabout 60 mm, a parameter d of about 16 mm, a parameter G of about 29 mm,and a parameter t of about 25 mm.

The holed cake was placed on a hearth in a high-temperature furnace.According to the reduction reaction conditions in Table 4, the maximumreduction reaction temperature in the high-temperature furnace was 1450°C. and the reduction reaction time was 35 min.

As shown in Table 4, the metal iron conversion rates obtained with thesample Nos. C-1, C-2 and C-3 are 90.5%, 83.2% and 95.5%, respectively.The yields of the metal iron are 90.2, 62.4, and 69.6 Kg-M.Fe/(h*m²)respectively.

It can be found through comparison of Embodiment 1 with the comparativeexample that when the reduction reaction is carried out with a holedcake, the reduced iron can be obtained with a comparable rate ofconversion to metal iron at a low carbon/oxygen ratio (C/O), a lowreduction reaction temperature, and with a short reduction reactiontime, and the yield of metal iron is also increased considerably.

Embodiment 2

In Embodiment 2 of the present disclosure, the reduction reaction wascarried out with a holed cake. Table 5 shows the reduction reactionconditions and the characteristics of the reduced iron produced inEmbodiment 2 of the present disclosure.

TABLE 5 Reduction reaction conditions and characteristics of the reducediron produced in Embodiment 2 of the present disclosure. Metal ironSample Metal oxide conversion rate Yield of metal iron No. mineral No.Reduction reaction condition (%) Kg-M.Fe/(h * m²) C-4 Waste oxideCarbon/oxygen ratio (C/O) = 1.0 91.8 72.2 #01 Reaction temperature:1350° C. Reaction time: 45 min C-5 Mineral #01 Carbon/oxygen ratio (C/O)= 1.0 81.1 52.0 Reaction temperature: 1350° C. Reaction time: 45 min C-6Mineral #02 Carbon/oxygen ratio (C/O) = 1.0 88.6 57.3 Reactiontemperature: 1350° C. Reaction time: 45 min

In Embodiment 2, the same raw materials are used, and the reductionreaction conditions are changed, in which the reduction reactiontemperature drops from 1450° C. to 1350° C., and the reduction reactiontime is prolonged from 35 min to 45 min, as compared with Embodiment 1of the present disclosure.

In Embodiment 2, the metal iron conversion rate is high for the sampleNo. C-1 and slightly low for sample Nos. C-5 and C-6; however, thereduced ion still has a high metal conversion rate, compared withEmbodiment 1 of the present disclosure.

In Embodiment 2, the yield of the metal iron is low compared withEmbodiment 1 of the present disclosure. The reason is that the reductionreaction time is prolonged, causing the yield of the metal iron todecrease. However, although the yield of the metal iron in Embodiment 2of the present disclosure is lower than that in Embodiment 1 of thepresent disclosure, it is still higher than that in the comparativeexample.

In Embodiments 1 and 2, the reduction reaction is carried out with aholed cake, through which both a high metal iron conversion rate and ahigh yield of the metal iron are achieved. Moreover, the usage of thecarbonaceous reducing agent is correspondingly reduced. Mostimportantly, the reduction reaction temperature is reduced from 1500 to1350° C., which is an important breakthrough in the ironmakingtechnology.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, and composition of matter, means, methods and stepsdescribed in the specification. As those skilled in the art will readilyappreciate form the present disclosure, processes, machines,manufacture, compositions of matter, means, methods, or steps, presentlyexisting or later to be developed, that perform substantially the samefunction or achieve substantially the same result as the correspondingembodiments described herein may be utilized in accordance with someembodiments of the present disclosure.

Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, and compositions of matter,means, methods or steps. In addition, each claim constitutes a separateembodiment, and the combination of various claims and embodiments arewithin the scope of the invention.

What is claimed is:
 1. A method for producing metal from metal oxide bycarbothermic reduction, comprising: providing a holed cake having acomposition comprising a metal oxide, a carbonaceous reducing agent, anda binder, and the holed cake having a plurality of holes; and placingthe holed cake in a high-temperature furnace for carbothermic reduction,to reduce the metal oxide in the holed cake into a metal.
 2. The methodof claim 1, wherein the holed cake is prepared by the following steps:the metal oxide, the carbonaceous reducing agent and the binder areuniformly mixed to form a mixture; and then the mixture is disposed in amold to form the holed cake.
 3. The method of claim 1, wherein thecontent of the metal oxide is 70 to 90 wt % inclusive.
 4. The method ofclaim 1, wherein the content of the carbonaceous reducing agent is 10 to30 wt % inclusive.
 5. The method of claim 1, wherein the binder is addedin an amount of 0.1 to 6% based on the total weight of the metal oxideand the carbonaceous reducing agent.
 6. The method of claim 1, whereinthe metal oxide is iron oxide, nickel oxide, copper oxide, lead oxide,manganese oxide, tin oxide, potassium oxide, sodium oxide, zinc oxide,or a combination of at least two of the foregoing.
 7. The method ofclaim 1, wherein the carbonaceous reducing agent is carbon black,activated carbon, coal, coke, graphite, charcoal, or a combination of atleast two of the foregoing.
 8. The method of claim 1, wherein each ofthe holes has a center, and a distance exists between the centers of twoadjacent holes.
 9. The method of claim 8, wherein a to-be-reducedmaterial portion is between two adjacent holes, the to-be-reducedmaterial portion has a thickness, and the thickness of the to-be-reducedmaterial portion is less than the distance.
 10. The method of claim 1,wherein a reaction temperature of the carbothermic reduction is 900 to1600° C. inclusive.
 11. The method of claim 1, wherein a reaction timeof the carbothermic reduction is 30 to 80 min inclusive.
 12. A holedcake has a composition comprising a metal oxide, a carbonaceous reducingagent, and a binder, and the holed cake has a plurality of holes. 13.The holed cake of claim 12, wherein the content of the metal oxide is 70to 90 wt % inclusive.
 14. The holed cake of claim 12, wherein thecontent of the carbonaceous reducing agent is 10 to 30 wt % inclusive.15. The holed cake of claim 12, wherein the binder is added in an amountof 0.1 to 6% based on the total weight of the metal oxide and thecarbonaceous reducing agent.
 16. The holed cake of claim 12, wherein themetal oxide is iron oxide, nickel oxide, copper oxide, lead oxide,manganese oxide, tin oxide, potassium oxide, sodium oxide, zinc oxide,or a combination of at least two of the foregoing.
 17. The holed cake ofclaim 12, wherein the carbonaceous reducing agent is carbon black,activated carbon, coal, coke, graphite, charcoal, or a combination of atleast two of the foregoing.